lactic acid bacteria

general charatceristic of lactic acidn bacteria

Shape	Rod or cocci
Spore-forming	Non-spore forming
Gram	+
Oxygen	Aerotolerant anaerobes
Other	1.     They convert simple sugar(fructose, lactose, galactose, maltose)--- lactic acid and organic acid

what is the main substrate for lactic acid bacteria

simple fermentable sugar: pentose and hexoses

why lactic acid bacteria is a good competitor

1. it is a fast grower which consume nutrtients fast and outcompete other microbes

2. produce acid inhibit the growth of other microbes

is lactic acid bacteria an energy efficient microbes?

• no they are not

• since they cannot fully degrade the simple sugar into carbon dioxide and water

what are the 3 types of lactic acid bacteria fermentation

1. homofermentative (mix acid, homo)

2. heterofermentative (O2 or not)

3. falcultative heterofermentative

what is te enzyme used in homofermentation and type of substrate it consume?

• aldolase

• hexsoses

example of microbes in homofermentation?

• lactococcus

• pediococcus

• streptococcus

what is EM pathway

• convert the hesose—-2 pyruvate +2 ATP +2NADH

describe the EM pathway

Overall: glucose----2 pyruvate + 2 ATP

1.     Glucose will be oxidized by NAD+ and break down into TP3

2.     Then TP3 will be convert into intermediate product pyruvate, and 2 ATP will be formed.

Based on the environmental condition, pyruvate will from homolactic or mixed acid

when will LAB switch from homo to mixed acid fermentation

1. Limit substrate in the environment.

2. Slow growth of the microbes

what is the production from homo and mixed acid fermentation

Homo: pyruvate (EMP)—-lactate+2ATP

Mixed acid: pyruvate (EMP)—-lactate+ acetate+ formate+ethanol +2.5ATP

what is the benefit of switching to mixed acid fermentation?

• generate 0.5 more ATP, benefit microbial growth

what is the enzyme and substrate used in heterofermentation

• phosphoketolate

• pentose/hexose (but 6-p gluconate need to convert to pentose)

example microbes in heterofermentation

leuconostoc

what is 6-P gluconate

• Convert heoxoses to pentose(Glucose---gluconate—-pentose )

• through oxidation and decarboxylation

what is the phosphoketolase pathway

1.     Phsophoketolase will break down pentose into TP3 and acetyl-P

2.     TP3 —- pyruvate —- lactate

3.     Acetyl-P will convert to different molecules based on the oxygen avalibility

• O2: acetate + carbon dioxide + ATP

• NO: ethanol + ATP

How to distinguish between hetero and mixed acid (homo) fermentation

-              check whether there is carbon dioxide production

-              Since only heterofermentation will produce carbon dioxide

what is falculatative fermentation

• Facultative heterofermentater contain both aldolase and phosphoketolase

• they can switch between homofermentation and heterofermentation based on the substrate availability in the surrounding medium

example of microbes

lactobacillus

what are the functions of the metabolite generate by the LAB

• lactic acid: acidification, inhibit the growth of spoilage microbes

• citrate: addition of aroma compounds to food

• carbon dioxide: formation of eye in the cheese production

which LAB are thermophilic

streptococcus and lactobacillus

which are homo and hetero

homo: lactococcus, lactic, lactic diacetylatic, streptococcus, latobacillus.

hetero: leuconostoc

what does L and DL mean in mesophilic

L: contain lactis cermoris

DL: contain both lactis cremrois ad diacetylactis

food product

Product	L	DL	O	Thermophilic
Butter	+	+
Sour cream	+	+
Yoghurt				+
Cheddar cheese	+	+	+